Getter Material And Evaporable Getter Device Using The Same, And Electron Tube

ABSTRACT

The present invention provides a getter material configured by a pressed powder mixture comprising Ba—Al alloy powder and Ni powder, wherein when the pressed powder mixture is heated in a vacuum atmosphere or an inert gas atmosphere, a temperature at which an exothermic reaction starts is ranging from 750° C. to 900° C. According to this getter material, since the temperature at which the pressed powder mixture starts the exothermic reaction is set within a range from 750° C. to 900° C., there can be provided a getter material and an evaporation type getter device capable of suitably controlling an evaporation amount of getter components under a stable condition, and is excellent in responsiveness because a time ranging from a starting time of heating the getter material to a starting time of evaporation of the getter components can be shortened. In addition, the metal container to be filled with the getter material is free from deformation and melting, and a heat-evaporation process time of the getter material can be shortened, so that there can be provided the evaporation type getter device excellent in responsiveness because a time required for the electron tube to attain to a predetermined vacuum degree can be also shortened.

TECHNICAL FIELD

The present invention relates to a getter material, which is used forrealizing a vacuum state required for an electron tube by absorbing anunnecessary gas components containing in the electron tube such as acathode ray tube, and also relates to an evaporation type getter deviceand an electron tube using the getter material. More particularly, Thepresent invention relates to a getter material, an evaporation typegetter device and an electron tube using the same capable of suitablycontrolling an evaporation amount of getter components under a stablecondition, and is excellent in responsiveness because a time rangingfrom a starting time of heating the getter material to a starting timeof evaporation of the getter components is short.

BACKGROUND ART

Generally, when an electron tube such as cathode ray tube (CRT) or thelike is operated under a condition where a vacuum pumping from inside ofthe electron tube is insufficient, such insufficient vacuum degree hasan adverse influence on characteristics of the electron tube. Therefore,in the electron tube, there is provided a getter device for sufficientlyremoving unnecessary gas components from the inside of the electrontube.

In recent years, for example, in a technical field of television (TV)for civil applications, a large-screen TV set having a screen size ofabout 32 to 37 inches has become widely used. Under this situation, theCRT to be used for such the large-screen TV has been increased in sizethereof. In such a large-sized electron tube, number of,parts to beassembled into the tube is also increased. Simultaneously, a volume ofthe electron tube is also further increased.

Therefore, it becomes more and more important to improve thecharacteristics per se and stability of the characteristics of thegetter device for maintaining a high degree of vacuum in the electrontube by adsorbing both: a residual gas remained in the electron tubeafter completion of the vacuum-pumping operation using a vacuum pump inthe electron tube manufacturing process; and the unnecessary gascomponents released from respective parts including a vacuum chamberarranged in the electron tube.

Concretely, for the purpose of absorbing the unnecessary gasses releasedin the electron tube, the electron tube typically represented by CRT isequipped with an evaporation type getter device which is manufacturedby: preparing a getter material consisting of a mixture of Ba—Al alloypowder containing Ba, Al as main component and Ni powder; and fillingthe getter material into a metal container formed of an alloy such asiron, steel, Ni alloy, stainless steel.

In this getter device, when the getter material consisting of themixture of Ba—Al alloy powder and Ni powder is heated to rise atemperature thereof, an exothermic reaction of bringing Al component andNi component into combination is started at a predetermined constanttemperature, Ba component contained in the getter material is vaporized(getter-flashed), and an impurity-gas adsorbing function is exhibited bythe Ba component. As a result, a degree of vacuum in the electron tubecan be maintained to a predetermined value.

Accordingly, the getter device equipped in the electron tube is requiredto evaporate a predetermined amount of Ba (barium) by which theunnecessary gasses contained in the electron tube is absorbed thereby toincrease the degree of vacuum in the electron tube. Therefore, when theamount of the evaporated Ba is small, the predetermined degree of vacuumrequired for the electron tube cannot be obtained.

On the other hand, when the amount of evaporated Ba is excessivelylarge, Ba-amount to be adhered to structural members such as inner wallor the like of the electron tube also becomes excessively large.Therefore, the excess amount of Ba becomes a cause of inviting troublessuch that an abnormal discharge is liable to occur and a part of Baadhered to the inner wall is dropped and adhered to another portionwithin the electron tube thereby to obstruct a normal operation of theelectron tube. Accordingly, it is technically important to control theamount of evaporated Ba so as to be within a predetermined rangerequired for the electron tube.

However, in the conventional getter materials, although a temperature atwhich the exothermic reaction of the getter material starts has a greatinfluence on Ba evaporation amount, such a technical fact has not beenrecognized at all. In addition, needless to say, a range of theexothermic reaction starting temperature has not been clearly determinedto a specified range. Therefore, a dispersion or scattering of theexothermic reaction becomes large, so that there has been posed aproblem that the Ba evaporation amount cannot be sufficientlycontrolled.

Further, in general, the getter material is filled into a metalcontainer having an opening portion called a getter ring for evaporatingthe Ba component, and the getter material is actually used in the packedstate. However, when the exothermic reaction starting temperature isexcessively high, there has been also posed problem that a thermaldeformation and melting of the metal container per se are liable tooccur, so that the evaporation of Ba cannot be performed with a stablecondition.

As a method of evaporating Ba from the getter device equipped in theelectron tube, there has been generally adopted a method in which apredetermined radio frequency induction generated by radio frequencyinduction power is applied from an outside of the electron tube to thegetter material disposed in the electron tube under a non-contactingstate thereby to heat the getter material.

According to this heating method, there can be provided tangibleadvantages that the getter material can be heated under a conditionwhere the heating operation would not affect to other portions exceptthe getter device in the electron tube sealed in a vacuum condition, andit is easy to rapidly heat the getter material whereby a process timerequired for producing the electron tube can be shortened, thus beingadvantageous for the process of manufacturing the electron tube.

However, in the above heating method by applying the high-frequencymagnetic field, the metal container filled with the getter material isalso heated at the time of heating the getter material. At this time, arelationship between a specification of the metal container and radiofrequency induction heating conditions have not been paid attention atall in the conventional getter device, so that there have been alsoposed the following problems. Namely, in a case where a ratio forheating the metal container by the radio frequency induction power isremarkably larger than that for heating the getter material, atemperature rise of the metal container becomes greatly larger than thatof the getter material, so that the metal container is easily deformedand molten before the exothermic reaction of the getter material isstarted.

As a result, there is posed a problem such that it becomes difficult tostably evaporate the getter component, and the temperature rise of thegetter material per se is delayed. In addition, it requires a longheating-evaporation process time for the getter material to obtain asufficient evaporation amount of Ba so as to attain a predeterminedvacuum degree in the electron tube. In other words, the evaporationamount of Ba corresponding to the heating time and responsiveness untilthe predetermined degree of vacuum is obtained are lowered, thus being abottleneck problem. On the other hand, there has been also posed aproblem that when the heating-evaporation process time is set to beshort, the amount of evaporated Ba is insufficient, so that it becomesdifficult to obtain the vacuum degree required for the electron tube.

The present invention had been achieved to solve the aforementionedproblems, and an object of the present invention is to provide a gettermaterial, an evaporation type getter device and an electron tube capableof suitably controlling an evaporation amount of getter components undera stable condition, and is excellent in responsiveness because a timeranging from a starting time of heating the getter material to astarting time of the evaporation of the getter components is short.(i.e., the evaporation amount of Ba corresponding to the heating timeand responsiveness until the predetermined degree of vacuum is obtainedare excellent.)

Another object of the invention is to provide an evaporation type getterdevice and an electron tube using the getter device in which the metalcontainer to be filled with the getter material is free from deformationand melting, and a heat-evaporation process time of the getter materialcan be shortened, so that there can be provided the evaporation typegetter device excellent in responsiveness because a time required forthe electron tube to attain to a predetermined vacuum degree can be alsoshortened.

DISCLOSURE OF THE INVENTION

In order to achieve the aforementioned objects, the inventors of thepresent invention had assembled various getter devices through a methodcomprising the steps of: preparing material powders having various grainsizes; pressing the material powder at various molding pressures to formgetter materials; preparing metal containers having various thickness;and filling the getter materials into the metal containers thereby toassemble the various getter devices.

With respect to thus assembled getter devices, the following points wereinvestigated. Namely, there were comparatively reviewed the influencesof the conditions such as the exothermic reaction starting temperatureof the getter material or the like onto a size of evaporation amount ofthe getter material, controllability and stability of the evaporation,responsiveness indicated by a heating time required for the gettercomponent to start evaporating, and a possibility of deformation ormelting of the metal container or the like.

As a result, the following technical findings were firstly obtained.That is, particularly, when a material powder having a predeterminedfine grain size is molded at a predetermined molding pressure to form apressed powder mixture and an exothermic reaction starting temperatureof the pressed powder mixture is limited to within a specified range, itbecame possible to adequately control the evaporation amount of thegetter components under a stable state, and there could be obtained agetter material and an evaporation type getter device excellent inresponsiveness because a time ranging from a starting time of heatingthe getter material to a starting time of evaporation of the gettercomponents is short.

In addition, when a thickness of the metal container, for being filledwith the getter material, which is made from an alloy mainly composed ofFe or Ni, and a frequency of the radio frequency induction for heatingthe getter material and evaporating Ba component from the gettermaterial, are adjusted so as to have a predetermined relation, there canbe provided an evaporation type getter device in which the metalcontainer is free from deformation and melting, and a heat-evaporationprocess time of the getter material can be shortened, so that there canbe provided the evaporation type getter device excellent inresponsiveness because a time required for the electron tube to attainto a predetermined vacuum degree can be also shortened. The presentinvention had been achieved on the basis of the above findings.

Namely, the getter material according to the present invention isconfigured by a pressed powder mixture comprising Ba—Al alloy powder andNi powder, wherein when the pressed powder mixture is heated in a vacuumatmosphere or an inert gas atmosphere, a temperature at which anexothermic reaction starts is ranging from 750° C. to 900° C.

The Ba—Al alloy powder constituting the above getter material is notlimited to BaAl₄ alloy powder. As far as a material takes an exothermicreaction between Ni component and Al component thereby to form a Ni—Alalloy and simultaneously evaporates Ba as the getter component, suchmaterial can be used. Such exothermic reaction is liable to occur whenBa—Al alloy and Ni are mixed as fine powder materials and heated thepowder mixture.

In this regard, Ni powder having a grain size of 10 μm is easilyavailable as carbonyl nickel. On the other hand, Ba—Al alloy powder ismanufactured through a method in which Ba and Al compound is molten andsolidified to form an alloy ingot, then the alloy ingot is pulverized.At this time, BaAl₄ as an intermetallic compound becomes brittle, sothat the pulverizing operation of BaAl₄ can be easily performed.

In view of the pulverizing operation, it is not always necessary to useBaAl₄ compound having a strict stoichiometric composition as the Ba—Alalloy, alloy material having a composition close to BaAl₄ may also besuitably used. Concretely, it is also suitable to use a Ba—Al alloyhaving a composition ranging from a composition in which an Al massratio is 10% larger than Al amount in the composition of BaAl₄ to acomposition of BaAl₂. More concretely, it is also suitable to use aBa—Al alloy powder containing an Al amount of 27-50% in terms of massratio.

In the above getter material, when the getter material composed of thepressed powder mixture comprising: BaAl₄ alloy powder mainly composed ofBa and Al of BaAl₄; and Ni powder is heated and temperature thereof isincreased, Ni component reacts with Al component in accordance with anexothermic reaction formula (1). Simultaneously, Ba component isevaporated and absorb impurity gasses thereby to exhibit a function ofthe evaporation type getter device.BaAl₄+4Ni→4NiAl+Ba   (1)

As is clear from the above exothermic reaction formula, a mass ratio ofBaAl₄ alloy powder and Ni powder is generally set to a value of 50%:50%.In the exothermic reaction of the getter material, there may be a casewhere an alloy having a composition in which Ni:Al ratio is other than1:1 is formed, or all of Ba contained in Ba—Al is not evaporated and apart of Ba is remained as an alloy having a composition different fromthat of BaAl₄. Therefore, depending on a condition of the gettermaterial, a condition of the getter device in which the getter materialis filled into the metal container, or conditions of temperature appliedto the getter material and heating time, the amount of Ba evaporation isgreatly different even if the same getter material is used at the sameamount in the getter device.

In the getter material of the present invention, when the gettermaterial configured by the pressed powder mixture is heated in a vacuumatmosphere or an inert gas atmosphere, a temperature at which anexothermic reaction starts in the pressed powder mixture is specified towithin a range from 750° C. to 900° C.

When this exothermic reaction starting temperature is lower than 750°C., Ba as the getter component is liable to excessively evaporate at alow temperature, so that it becomes difficult to control the evaporationamount of Ba. Simultaneously, the getter component is easily react inthe air, so that even if a heating operation at a low temperature, whichis required for assembling process of the electron tube, is performed,the getter component is easily damaged by oxidization or the like.

On the other hand, in a case where the exothermic reaction startingtemperature is excessively high so as to exceed 900° C., a heatingenergy amount required to be applied to the getter material becomeslarge, so that a time span ranging from a start of heating to a start ofthe exothermic reaction is prolonged, and a sufficient amount ofevaporated getter component cannot be obtained in a short time. In alsothis case, it becomes difficult to control the evaporation amount perse, and a response time until a predetermined vacuum degree is attainedin the electron tube is delayed. Accordingly, the above exothermicreaction starting temperature is specified in the range of 750° C. to900° C.

In this connection, when the grain sizes of BaAl₄ alloy powder and Nipowder to be mixed for preparing a getter material are set to anextremely fine region of about 1 μm or less, it is possible to lower theexothermic reaction starting temperature per se to be lower than 700° C.thereby to increase an evaporation amount of the getter component.However, as previously mentioned, Ba—Al alloy powder has a property ofbeing easily deteriorated in the air due to reaction such as oxidizationor the like. In a process of manufacturing the electron tube, the getterdevice containing Ba—Al alloy powder is attached in the electron tube.Thereafter, the electron tube is made vacuous. During the abovemanufacturing processes, the getter device is exposed to the air.Therefore, it is extremely difficult to actually prevent the getterdevice from being deteriorated by air.

Further, in a process of manufacturing CRT, there is a case where thegetter device is exposed to a high temperature air in a glass fritprocess for assembling a face portion and a funnel portion of CRT priorto make vacuum although the high temperature condition is varied inaccordance with a portion to which the getter device is provided. Atthis time, since Ba—Al alloy such as BaAl₄ or the like has a highreactivity, the deterioration of Ba—Al alloy due to oxidization isunavoidable to some extent.

In particular, when the grain size of the Ba—Al alloy powder isextremely fine region to be 1 μm or less, the deterioration phenomena ofthe alloy becomes abruptly notable, thereby to greatly lower theperformance of the getter device. Therefore, a weight ratio of theextremely fine BaAl₄ alloy powder having a grain size of 1 μm or lesscontained in an entire BaAl₄ alloy material powder is preferablycontrolled to 10 wt % or less. On the other hand, Ni powder is hardlydegraded by oxidation in comparison with BaAl₄ alloy powder, so that itis unnecessary to specify a lower limit of the grain size thereof.

According to thus configured getter material, since the temperature atwhich the pressed powder mixture starts the exothermic reaction is setwithin a range from 750° C. to 900° C., there can be provided a gettermaterial and an evaporation type getter device capable of suitablycontrolling an evaporation amount of getter components under a stablecondition, and is excellent in responsiveness because a time rangingfrom a starting time of heating the getter material to a starting timeof evaporation of the getter components can be shortened. In addition,the metal container to be filled with the getter material is free fromdeformation and melting, and a heat-evaporation process time of thegetter material can be shortened, so that there can be provided theevaporation type getter device excellent in responsiveness because atime required for the electron tube to attain to a predetermined vacuumdegree can be also shortened.

In an electron tube such as CRT or the like using the above evaporationtype getter device, it is required to evaporate a predetermined amountof Ba as a getter component (gas adsorbing component) for increasing avacuum degree in the electron tube by absorbing the impurity gassesremained inside of the electron tube body or by adsorbing an unnecessarygas generated from the respective parts including a vacuum chamberconstituting the electron tube.

In this regard, when the amount of evaporated Ba is small, a vacuumdegree required for the electron tube cannot be obtained. In contrast,when the amount of evaporated Ba is excessively large, the amount of Baadhered to an inner wall of the electron tube is also excessively large,thereby to cause an abnormal discharge. In addition, a part of theadhered substance would fall down from the inner wall of the electrontube and the fallen substance will adhere to another portion in theelectron tube, thus being a cause of having troubles in a normaloperation of the electron tube. Therefore, it is technically importantto control the amount of Ba evaporation to within a predetermined rangerequired for the electron tube.

In contrast, in the conventional getter material, since the exothermicreaction starting temperature have not been determined to a suitablerange, a scattering of the exothermic reaction becomes large, and it wasdifficult to sufficiently control the Ba evaporation amount. Further,the getter material has been used in a form in which the getter materialis filled into a metal container having an opening surface, so called agetter rings through which the Ba is evaporated. When the exothermicreaction starting temperature is excessively high, there has been alsoposed problems such that the metal container is easily deformedthermally and molten.

Further, the getter material is formed as a press-molded body obtainedby press-molding a mixture composed of Ba—Al alloy powder such as BaAl₄or the like and Ni powder. However, the exothermic reaction startingtemperature of the press molded body varies in accordance with acomposition ratio of Ni powder and Ba—Al alloy powder such as BaAl₄ orthe like contained in the getter material, grain sizes of the respectivematerial powders, molding pressure for press-molding a material mixture.It may be considered that the exothermic reaction starting temperatureshould be a low temperature, because a time required for heating thegetter can be shortened and the problem of the melting of the metalcontainer can be eliminated. However, in the actual getter material, arelationship between the exothermic reaction starting temperature andthe Ba evaporation amount has not been clear, so that the Ba evaporationamount cannot be suitably controlled.

In contrast to this, in the getter material and the evaporation typegetter device using the material according to the present invention inwhich the getter material composed of a mixed body comprising the Ba—Alalloy powder such as BaAl₄ or the like and Ni powder, when theexothermic reaction starting temperature is set to a range 750° C. to900° C., it was found that a time range from a time when the getterstarted to be heated by radio frequency induction until a time when theBa component starts evaporating can be shortened and the evaporationamount of Ba can be attained to within a predetermined stable range. Thepresent invention had been achieved on the basis of the above findings.

When the grain size of the Ba—Al alloy powder such as BaAl₄ or the likeand Ni powder is set to be fine, the exothermic reaction startingtemperature of the getter material used in the above getter device isshifted to a low temperature side. In contrast, when the grain size isset to be large, the exothermic reaction starting temperature is shiftedto a high temperature side. This is because a contact surface areabetween the Ba—Al alloy powder and Ni powder is increased due to thefine grain size of the material powders, thereby to allow the exothermicreaction starting temperature of the Ba—Al alloy powder such as BaAl₄ orthe like and Ni powder to shift to the low temperature side.

In this regard, when the grain sizes of both the Ba—Al alloy powder suchas BaAl₄ or the like and Ni powder are set to 10 μm or less, it becomespossible to prepare a getter material having the exothermic reactionstarting temperature of 750° C. or lower than 700° C. However, the Ba—Alalloy powder such as BaAl₄ or the like and Ni powder are chemicallyactive materials inherently. Therefore, when the powder has a grain sizeof 1 μm or less, there has been posed a problem such that a property ofthe powder is easily varied and degraded by oxidation thereof even underan ambient atmosphere (air condition) to which electron tube parts areexposed during a manufacturing process of the electron tube.

Therefore, in the present invention, in order to maintain a stableproperty within a process condition for manufacturing the electron tubeto which the getter device is equipped, an average grain size of theBa—Al alloy powder is set to 44 μm or less (it is preferable that a massratio of the fine Ba—Al alloy powder such as BaAl₄ or the like having agrain size of 1 μm or less contained in the BaAl₄ material powder is 10mass % or less.), or the grain size of the Ba—Al alloy powder is set towithin a range from several tens microns to 150 μm. In this regard, itis preferable that a maximum grain size is 300 μm or less. When theaverage grain size of the Ba—Al alloy powder is set to within the aboverange, it was confirmed that a sufficient evaporation amount of Ba canbe stably obtained within the exothermic reaction starting temperatureof 750° C. to 900° C.

On the other hand, Ni powder has more stable property and is lessdeteriorated by oxidation than the Ba—Al alloy powder such as BaAl₄ orthe like under a manufacturing environment of the electron tube, so thatthere is caused no problem even if the grain size of Ni powder is small.However, it was confirmed that Ni powder having a grain size of 10 μm orless is preferable for the purpose of increasing the contact surfacearea contacting Ba—Al alloy powder thereby to improve a reactivity withthe Ba—Al alloy powder.

Further, the following findings were also obtained. Namely, when amixing ratio (mass ratio) of the BaAl₄ powder and Ni powder was set to48:52-56:44, a maximum evaporation amount of Ba was obtained. In thisconnection, in a case where a Ba—Al alloy powder of which composition issomewhat deviated from that of BaAl₄ powder, Al mixing ratio withrespect to Ni is preferably set to almost the same range as in BaAl₄alloy.

Furthermore, when taking the contacting area between the Ba—Al alloypowder and Ni powder into consideration, it is preferable to use apowder in which a mass ratio of the Ba—Al alloy powder having a grainsize (absolute value) of 1 μm or less is less than 10% and the maximumgrain size thereof is 300 μm or less. On the other hand, it ispreferable to use a Ni powder having a maximum grain size of 20 μm orless and an average grain size of 10 μm or less.

Still further, as to the Ni powder for the getter material, it ispreferable to use a Ni powder in which a mass ratio of the Ni powderhaving a grain size of 20 μm or more is less than 10%. When the grainsize of Ni powder is excessively large, the contacting area between theBa—Al alloy powder and Ni powder becomes small, so that the exothermicreaction starting temperature is disadvantageously arisen whereby theevaporation amount of Ba is liable to be insufficient. Accordingly, itis preferable to use a Ni material powder in which a mass ratio of theNi powder having a grain size of 20 μm or more is less than 10%.

Further, in the above getter material, it is preferable that the pressedpowder mixture is a press-compacted body shaped by press-compacting apower mixture comprising the Ba—Al alloy powder and the Ni powder at acompacting pressure of 400 MPa or more.

In a case where the pressed powder mixtures each having the samecomposition of BaAl₄ alloy powder and Ni powder were manufactured asgetter materials by a pressure-compacting method in which the compactingpressure is set to a predetermined pressure or lower, the exothermicreaction starting temperature is abruptly raised in some gettermaterials, and the getter materials formed at the specified compactingpressure or higher have a relatively stable exothermic reaction startingtemperature.

In the getter materials manufactured by the press-compacting method inwhich BaAl₄ powder having an average grain size of 44 μm or less orhaving a grain size of several tens microns to 150 μm and Ni powderhaving a grain size of 10 μm or less were used, when a compactingpressure of 400 MPa or higher was applied, the exothermic reactionstarting temperature in a predetermined range could be obtained.

In contrast, in a case where the grain size of Ni powder was set to arange of 10 to 20 μm, the exothermic reaction starting temperature isincreased at the molding pressure of less than 1000 MPa, so that theexothermic reaction starting temperature of 750° C. to 900° C. at whicha stable evaporation amount of Ba could be obtained. Accordingly, forthe purpose of obtaining a suitable evaporation amount of Ba, it istechnically important to suitably control the compacting pressure inaccordance with the grain sizes of the material powders for the gettermaterial.

The evaporation type getter device according to the present invention isconfigured by comprising: a metal container; and a getter material as apress-compacted body filled in the metal container.

It is important that the above getter material is filled in the metalcontainer so as to tightly contact the metal container and so as not toform a gap between the metal container and the filled getter material.When the gap is formed between the metal container and the filled gettermaterial, a possibility of falling down of an entire getter material ora part of the getter material as the press-compacted body is increased.Even if a small amount of the getter material is fallen down, thefalling down may be a cause of abnormal discharge or clogging of shadowmask holes, thus resulting in lowering in performance of the electrontube.

An operation for evaporating Ba from the getter device equipped to theelectron tube is performed in accordance with an operating system inwhich a high frequency magnetic field caused by a predetermined highfrequency electric power is applied in non-contacting state from outsidethe electron tube to the getter device provided in the electron tubethereby to heat the getter material. According to this system, there canbe provided the following advantages. Namely, in the electron tubesealed to be vacuum state, heat affection against portions other thanthe getter device can be mitigated, and only the getter device can belimitedly heated. In addition, it becomes easy to rapidly heating thegetter device, so that a process time required for producing theelectron tube can be shortened.

However, in a case where the getter material is heated by being appliedwith the radio frequency induction, not only the getter material butalso the metal container filled with the getter material aresimultaneously heated. In this point, in the conventional getter device,a relationship between this metal container and the radio frequencyinduction heating condition has not been paid attention at all.Therefore, there have been posed the following problems.

Namely, in a case where a heating ratio to the metal container by meansof the radio frequency induction power is greatly larger than a heatingratio to the getter material, a temperature rise of the metal containerbecomes greatly larger than that of the getter material. As a result,there is posed a problem such that the metal container is deformed ormolten before the exothermic reaction of the getter material starts,whereby the evaporation of Ba component is obstructed. In addition, thetemperature rise of the getter material is slow and delayed, so that aprocess time required for heating and evaporating the getter material isdisadvantageously prolonged.

To cope with these problems, the present invention adopts the followingcountermeasures. That is, a metal container for accommodating the gettermaterial is formed from alloys such as iron, steel, Ni alloy orstainless steel. Further, a thickness of the metal container and afrequency of the radio frequency induction power for heating the gettermaterial are controlled so as to have a specified relationship, so thatthere can be obtained an evaporation type getter device which isexcellent in responsiveness and free from deformation or melting of themetal container, and capable of shortening the process time for heatingand evaporating the getter material and capable of shortening the timeuntil the electron tube attains to a predetermined vacuum degree.

That is, the evaporation type getter device of the present invention ischaracterized by comprising: a metal container formed of at least onematerial selected from of Fe, Ni, Fe alloy and Ni alloy; and a gettermaterial composed of a pressed powder mixture of Ba—Al alloy powder andNi powder, the getter material being filled in the metal container,wherein when assuming that a plate thickness of the metal container is tcm while a frequency of alternate current induction for inductionheating and evaporating Ba component from the getter material is f Hz,the plate thickness t of the metal container and the frequency f ofalternate current induction satisfy a relation formula:t≦12.7/(f)^(1/2).

In a case where the getter device comprising the getter material and themetal container filled with the getter material is heated by beingapplied with a radio frequency induction which is generated by applyinga radio frequency induction power to a radio frequency induction coil, aheat energy inputted by the radio frequency induction power is appliedto the getter material and the metal container, respectively.

As a material for constituting the metal container, there can be usedvarious materials having an excellent structural strength and heatresistance, and having a sufficiently higher melting point than theexothermic reaction starting temperature of the getter material. Exampleof the materials may include: Fe, Fe-based alloy, Ni, Ni-based alloy, analloy member comprising Fe or Ni and at least one element selected froma group consisting of Fe, Ni, Cr and Mn.

As the alloy member, for example, a stainless steel or the like issuitably adopted. Particularly, as the stainless steel, there is used analloy of which amount of components such as Cr, Ni, Mn other than Fecontained in the alloy is several mass % to several tens mass %. Inaddition, for the purpose of increasing the structural strength or heatresistance of Fe or Ni, there can be also used an alloy material such aschrome steel to which about 1 to 5 mass % of Cr, Mn, Ni is added. Notes,Ni is added to only Fe-based alloy, while Fe is added to only Ni-basedalloy.

In a case where the radio frequency induction power generated by theradio frequency induction coil is applied to the metal container formedof the above metal materials, when the frequency (f Hz) of the highfrequency induction power and the plate thickness (t cm) of the metalcontainer are set within a range so as to satisfy a relation formula (2)hereunder, it has been confirmed that the high frequency induction poweris well applied to the getter material filled in the getter device, anda sufficient temperature rising rate can be obtained whereby theevaporation amount of Ba can be effectively secured without causing anydeformation or melting of the metal container.t≦12.7/(f)^(1/2)   (2)

In the above high frequency magnetic field generating device, when thethickness (t cm) of the metal container is larger than a valuecalculated in accordance with the above formula at a specified frequency(f Hz), the high frequency electric power is concentrated to the metalcontainer, so that an amount of the electric power applied to the gettermaterial becomes relatively small and the temperature rising rate of thegetter material is delayed whereby it becomes difficult to obtain apredetermined evaporation amount of Ba by the high frequency heating ina short time.

At this time stage, when the electric power is increased or the gettermaterial is continued to be further heated for a long time, the metalcontainer is heated to a temperature far exceeding a recrystallizationtemperature of the members constituting the metal container, so that themetal container causes a deformation or the temperature thereof isfurther increased thereby to melt the metal container. As a result, suchdefects will exert a bad influence on characteristics of the electrontube.

In this regard, as schematically shown in FIG. 1, the above metalcontainer (getter ring) 2 is formed in such a manner that a plain metalplate is subjected to a drawing work so as to form in a cylindricalshape having a bottom wall and a protrusion extending vertically at acentral portion of the metal container. The metal container comprises:an outer side wall 2 a having a thickness of t1; a bottom wall 2 bhaving a thickness of t2; an inner side wall 2 c having a thickness oft3; and a central top portion wall 2 d having a thickness of t4.

However, a rank order of degrees of heat affections exerted on themembers by the radio frequency induction heating operation is asfollows. Namely, a first rank is the outer side wall 2 a, while a secondrank is the bottom wall 2 b. Therefore, it is necessary for at least thethickness (t1) of the outer side wall 2 a and the thickness (t2) of thebottom wall 2 b to make thin so that the thicknesses are less than aplate thickness (t cm) calculated by the relation formula (2).

In this connection, for the purpose of making thermal heat capacities ofthe respective parts of the metal container (getter ring) 2 uniform andachieving an uniformity in heat affection exerted by the high frequencyheating in the entire container, it is preferable that all of thethicknesses t1, t2, t3 and t4 of the respective parts of the metalcontainer 2 should be made thin so that the respective thicknesses areless than a plate thickness (t cm) calculated by the relation formula(2).

An electrical resistivity of the getter material prepared bypress-molding a mixture of the Ba—Al alloy powder such as BaAl4 or thelike and Ni powder is higher than an electrical resistivity inherent tothe Ba—Al alloy such as BaAl₄ or the like and Ni. On the other hand, theelectrical resistivity of the metal container is equal to that of themetal material constituting the metal container.

In the getter material or the evaporation type getter device accordingto the present invention, it is preferable that a press-compacted bodyhas an electrical resistivity of 20 mΩ-cm or less. That is, when theelectrical resistivity of the getter material prepared bypress-compacting a mixture of the Ba—Al alloy powder such as BaAl₄ orthe like and Ni powder is excessively large so as to exceed 20 mΩ-cm anda getter device provided with a Ba-evaporating portion having a diameter(a minor diameter for a case where an outline shape of theBa-evaporating portion has non-round shape such as an oval shape or thelike) of 10 mm to several tens mm is generally used, an efficiency ofradio frequency induction heating is extremely deteriorated. Therefore,it is preferable that the press-compacted body has the electricalresistivity of 20 mΩ-cm or less.

The electrical resistivity of the getter material can be adjusted insuch a manner that material powders each having a different electricalresistance and grain sizes are appropriately combined to prepare apowder mixture and a compacting pressure for press-compacting the powdermixture is controlled. In this connection, when the grain size of thematerial powder is set to excessively fine, the electrical resistivityof the getter material becomes large, so that it becomes impossible toperform the radio frequency induction heating operation. Accordingly, itis technically important to use the Ba—Al alloy powder and Ni powderhaving the aforementioned grain size and the average grain size.

The electron tube according to the present invention is characterized bycomprising thus configured evaporation type getter device. According tothe electron tube of the present invention, the getter material can besufficiently evaporated and scattered in a stable condition even if thegetter device is applied to a large-scaled electron tube, thus greatlycontributing to improve quality and reliability of the large-scaledelectron tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically showing one embodiment ofa getter device formed by filling a getter material according to thepresent invention into a metal container.

FIG. 2 is a graph showing a relationship between a compacting pressurefor a getter material powder and an exothermic reaction startingtemperature of the getter material powder.

FIG. 3 is a graph showing a relationship between a compacting pressurefor a getter material powder and an exothermic reaction startingtemperature of the getter material powder in a case where other materialpowders each having a different specification are used.

FIG. 4 is a graph showing a relationship between a time ranging from aheating start to Ba-evaporation start and amount of the evaporation ofBa component when the getter material is heated for 30 seconds.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a getter material according to the present inventionwill be described hereunder with reference to the following Examples andComparative Examples together with drawings.

EXAMPLES 1-4 AND COMPARATIVE EXAMPLE 1

Ni material powder having an average grain size of 5 μm in which aweight ratio of Ni powder having a grain size of 20 μm or more is 5 mass% was prepared, while alloy powder having a composition of BaAl₄, grainsize of 44 μm or less and an average grain size of 31 μm was prepared.54 mass % of the Ni material powder and balance of the BaAl₄ alloypowder were blended thereby to prepare a powder mixture as a material ofgetter material for the respective Examples and Comparative Examples. Inthis regard, the average grain size and a maximum grain size of therespective powders for constituting the getter material were measured bya particle size distribution measuring operation based on asieve-screening method and a laser-scattering diffraction method.

Next, thus prepared material powder mixture was press-compacted atvarious compacting pressures shown in Table 1 thereby to prepare gettermaterials 3 each composed of a pressed powder mixture according toExamples 1-4 and Comparative Example 1. With respect to each of thesegetter materials 3 according to Examples and Comparative Example, anexothermic reaction starting temperature of the getter material 3 wasmeasured in accordance with a method using a differential thermogravimetric analyzer (DTA) in which the temperature of the gettermaterial 3 was risen from a room temperature at a temperature risingrate of 10° C./min.

The exothermic reaction starting temperature of the getter material 3could be easily measured as a heating temperature corresponding to apeak of heat generation amount. The peak of the heat generation amountwas formed during a continuous heating operation for heating the gettermaterial, and the peak was detected as a portion at which the heatgeneration amount was abruptly increased. In this regard, the gettermaterial of which the exothermic reaction starting temperature wasoutside of the range specified in this invention was determined asComparative Example 1.

Then, as shown in FIG. 1, there were prepared metal containers 2 eachcomposed of SUS304 provided with an outer peripheral wall 2 a having athickness t1 of 0.02 cm and a bottom wall 2 b having a thickness t2 of0.02 cm. 1.1 g of the getter material 3 was filled into each of themetal containers 2, and the filled getter materials 3 werepress-compacted at a pressing force which was the same pressure as thecompacting pressure used in the operation for measuring the exothermicreaction starting temperature of the getter material 3, so that thegetter materials 3 were press-contacted to the metal containers 2thereby to manufacture the respective getter devices of Examples 1-4 andComparative Example 1.

FIG. 1 is a cross sectional view schematically showing a cross sectionalstructure of the getter devices 1 of the respective Examples andComparative Example. Each of the getter devices 1 comprises: the metalcontainer 2 composed of SUS304 stainless steel and formed by a drawingwork; and the getter material 3 filled into a recessed portion of thismetal container 2 by a press-contacting operation.

Each of the getter devices 1 of Examples and Comparative Example asprepared above was heated by a radio frequency induction having afrequency of 300 kHz and a constant power strength, and a time rangingfrom a heating-start to Ba-evaporation-start and Ba evaporation amountafter heating for 30 seconds were measured. In this connection, Baevaporation amount was measured by a weight difference of the gettermaterial between before and after the evaporating operation. Themeasuring results of the Ba evaporation amount together with thecompacting pressure are collectively shown in Table 1 hereunder. TABLE 1Exothermic Ba Time from Reaction Evaporation Heating-Start CompactingStarting Amount After to Ba- Pressure Temperature Heating forEvaporation- Sample No. (MPa) (° C.) 30 sec. (mg) Start (sec)Comparative 1300 936 181 11.6 Example 1 Example 1 1450 883 230 9.4Example 2 600 842 237 9.1 Example 3 1000 811 235 9.0 Example 4 1200 782237 9.0

As is clear from the results shown in above Table 1, according to thegetter devices of Examples 1-4 in which the exothermic reaction startingtemperature of the getter materials composed of the respective pressedpowder mixtures are specified to within a predetermined range from 782°C. to 883° C., the evaporation amount of Ba after heating for 30 secondsis large, and the values of the evaporation amounts are also stable, sothat it was confirmed that the respective devices can exhibit anexcellent characteristic of evaporating the getter component. Inaddition, the time from heating start to Ba evaporation start was shortto be a level of 9 seconds or so in all Examples, so that it was alsoconfirmed that each of the getter devices has an excellentresponsiveness.

On the other hand, according to the getter device of Comparative Example1 prepared by filling a getter material into the metal container inwhich the exothermic reaction starting temperature of the gettermaterial was specified to an excessively high temperature so as toexceed 900° C., it was confirmed that Ba evaporation amount was rapidlylowered in comparison with those of Examples, and the time from heatingstart to Ba evaporation start was relatively prolonged so as to exceed11 seconds, so that it was also confirmed that the responsiveness of thegetter device of Comparative Example was surely inferior.

On the other hand, other than the above Comparative Example, there wasalso prepared a getter material in accordance with the followingprocedure. Namely, BaAl₄ alloy powder used in Examples were furtherfinely pulverized so as to have an average grain size of 10 μm or lesswhereby the exothermic reaction starting temperature of the gettermaterial was lowered to within a range of 700° C. to 740° C. Withrespect to the getter devices prepared by filling these getter materialsinto the metal containers, Ba evaporation amounts after heating for 30seconds were measured in the same manner as in Examples. As a result,the Ba evaporation amount was sufficient and stable in any cases.

However, in the getter device using this getter material, a degradationand deterioration of the getter material was rapidly advanced in theair. Therefore, the deterioration due to oxidation was rapidly advancedin a process of assembling the getter device into the electron tube. Asa result, a sufficient Ba evaporation amount could not be obtained in apractical use of the electron tube. Accordingly, it can be said that theexothermic reaction starting temperature of 750° C. or higher is morepreferable range for the practical use of the getter material.

EXAMPLE 5

As Example 5, getter materials of Samples 1-3 were prepared bypress-compacting three kinds of material powder mixtures each having adifferent grain size distribution at a compacting pressure of 800-1500MPa.

That is, the material powder mixture for Sample 1 was prepared inaccordance with the following procedures. Ni material powder having anaverage grain size of 6.5 μm in which a weight ratio of Ni powder havinga grain size of 20 μm or more is 5 mass % was prepared, while alloypowder having a composition of BaAl₄, maximum grain size of 150 μm andan average grain size of 77 μm was prepared. 53 mass % of the Nimaterial powder and balance of the BaAl₄ alloy powder were blendedthereby to prepare a powder mixture as a material of getter material forSample 1.

Further, the material powder mixture for Sample 2 was prepared inaccordance with the following procedures. Ni material powder having anaverage grain size of 13 μm in which a weight ratio of Ni powder havinga grain size of 20 μm or more is 8 mass % was prepared, while alloypowder having a composition of BaAl₄, maximum grain size of 150 μm andan average grain size of 77 μm was prepared. 53 mass % of the Nimaterial powder and balance of the BaAl₄ alloy powder were blendedthereby to prepare a powder mixture as a material of getter material forSample 2.

Furthermore, the material powder mixture for Sample 3 was prepared inaccordance with the following procedures. Ni material powder having anaverage grain size of 8 μm in which a weight ratio of Ni powder having agrain size of 20 μm or more is 13 mass % was prepared, while alloypowder having a composition of BaAl₄, maximum grain size of 150 μm andan average grain size of 77 μm was prepared. 53 mass % of the Nimaterial powder and balance of the BaAl₄ alloy powder were blendedthereby to prepare a powder mixture as a material of getter material forSample 3.

Thus prepared materials for the respective getter materials werecompacted at a compacting pressure of 800-1500 MPa as shown in FIG. 2thereby to prepare the respective getter materials for Samples. Then,the exothermic reaction starting temperature of the respective gettermaterials were measured in the same manner as in Example 1. The measuredresults are shown in FIG. 2.

As is clear from the results shown in FIG. 2, according to the gettermaterial of Sample 1, the exothermic reaction starting temperatures ofthe getter materials were within a range from 860° C. to 880° C. in acompacting pressure range of 800-1500 MPa, so that a suitableevaporation amount of the getter components could be expected.

On the other hand, according to the getter materials of Samples 1-2,when the materials were treated at low compacting pressure range of800-900 MPa, the exothermic reaction starting temperatures were abruptlyrisen, so that it was confirmed that the suitable evaporation amount ofthe getter components could not be expected. Nevertheless, when thecompacting pressure was set to 1000-1200 MPa in this case of Samples1-2, a predetermined exothermic reaction starting temperature wasobtained. Accordingly, when both the grain size of the material powderfor the getter material and the compacting pressure are suitablycontrolled, a suitable exothermic reaction starting temperatures can beobtained.

EXAMPLE 6

This Example 6 shows an example in which a powder mixture composed of Nimaterial powder and Ba—Al alloy powder each having a further finer grainsize than those of Example 5 was used as a material for the gettermaterial. That is, Ni material powder having an average grain size of4.5 μm in which a weight ratio of Ni powder having a grain size of 20 μmor more is 2 mass % was prepared, while BaAl₄ alloy material powdercontaining 35 mass % of BaAl₄ alloy powder having an average grain sizeof 44 μm and balance of BaAl₄ alloy powder having a grain size of 70-44μm was prepared. 53 mass % of the Ni material powder and balance of theBaAl₄ alloy material powder were blended thereby to prepare a powdermixture as a material of getter material for Example 6.

Thus prepared materials for Example 6 were compacted at a compactingpressure of 300-800 MPa as shown in FIG. 3 thereby to prepare therespective getter materials for Example 6. Then, the exothermic reactionstarting temperature of the respective getter materials were measured inthe same manner as in Example 1. The measured results are shown in FIG.3.

As is clear from the results shown in FIG. 3, according to the gettermaterial of Example 6, when the materials were treated at low compactingpressure range of 400-800 MPa, the exothermic reaction startingtemperatures were within a range of 800° C. to 900° C., so that it wasevident that the suitable evaporation amount of the getter componentscould be expected.

On the other hand, when the materials were treated at low compactingpressure of less than 400 MPa, the exothermic reaction startingtemperatures were abruptly risen, so that it was confirmed that thesuitable evaporation amount of the getter components could not beexpected.

EXAMPLES 7-9 AND COMPARATIVE EXAMPLES 2-4

Three kinds of getter material powder mixtures each having a differentgrain size distribution were prepared while two kinds of containers eachhaving a different plate thickness were prepared. Then, the respectivegetter material powder mixtures were filled into the respective metalcontainers and the mixtures were press-contacted to the metal containersthereby to manufacture the respective getter devices of Examples andComparative Examples. Thereafter, the characteristics of the respectivegetter devices were mutually compared.

That is, 54 mass % of Ni material powder having an average grain size of4.5 μm in which a weight ratio of Ni powder having a grain size of 20 μmor more is 2 mass %; 35 mass % of BaAl₄ alloy material powder having anaverage grain size of 44 μm; and balance of BaAl₄ alloy powder having agrain size of 53-44 μm were blended thereby to prepare a powder mixtureas a first material for the getter material (Example 7 and ComparativeExample 2).

Further, 50 mass % of Ni material powder having an average grain size of4 μm in which a weight ratio of Ni powder having a grain size of 20 μmor more is 3 mass %; 10 mass % of BaAl₄ alloy material powder having anaverage grain size of 44 μm; and balance of BaAl₄ alloy powder having agrain size of 44-53 μm were blended thereby to prepare a powder mixtureas a second material for the getter material (Example 8 and ComparativeExample 3).

Furthermore, 54 mass % of Ni powder having a grain size of 3-10 μm; 10mass % of BaAl₄ alloy material powder having an average grain size of 44μm or less; and balance of BaAl₄ alloy powder having a grain size of53-44 μm; were blended thereby to prepare a powder mixture as a thirdmaterial for the getter material (Example 9 and Comparative Example 4).

On the other hand, there were prepared two kinds of metal containers 2each having a shape as shown in FIG. 1, and the metal containers 2 areformed of SUS316 stainless steel in which all of portions including theouter side wall 2 a and the bottom wall 2 b has a plate thickness (t) of0.02 cm or 0.025 cm.

Then, 1.1 gram of the first to third materials was filled into the metalcontainers 2 formed of SUS316 and having a thin plate thickness (t) of0.02 cm. Subsequently, the filled materials were press-compacted at acompacting pressure of 1000 MPa, thereby to prepare the getter devicesof Examples 7-9.

On the other hand, 1.1 gram of the first to third materials was filledinto the metal containers 2 formed of SUS316 and having a thick platethickness (t) of 0.025 cm. Subsequently, the filled materials werepress-compacted at a compacting pressure of 1000 MPa, thereby to preparethe getter devices of Comparative Examples 2-4.

Each of the getter devices of Examples and Comparative Example asprepared above was heated by a radio frequency induction having afrequency of 330 kHz and a constant power strength, and a required timeranging from a heating-start time to Ba-evaporation-start time and Baevaporation amount after heating for 30 seconds were measured. Themeasuring results of the required time and Ba evaporation amount shownin FIG. 4 were obtained.

In this connection, when a plate thickness (t) of the metal container byapplying the frequency of 330 kHz of the radio frequency induction forheating the getter device to the relation formula (2) :t≦12.7/(f)^(1/2), a plate thickness of t (≦0.0221 ) cm is obtained.Accordingly, a specification of the getter devices of Examples 7-8 eachcomprising a thin metal container 2 having a plate thickness (t) of 0.02cm satisfies the relation formula (2).

On the other hand, a specification of the getter devices of ComparativeExamples 2-4 each comprising a thick metal container 2 having a platethickness (t) of 0.025 cm would not satisfy the relation formula (2).

As is clear from the results shown in FIG. 4, according to the getterdevices of Examples 7-8 using a thin metal container 2, the radiofrequency induction is effectively applied to the getter material filledin the metal container, and a sufficient temperature rising rate can beobtained, so that the evaporation amount of Ba after heating for 30seconds is sufficient. In addition, a required time ranging from theheating start time to Ba evaporation start time is less than 10 seconds,thus realizing an excellent responsiveness.

On the other hand, according to the getter devices of ComparativeExamples 2-4 each using the thick metal container, the generated heatwas not a little absorbed to the metal container and the temperaturerise of the getter material is delayed, so that the Ba evaporationamount is not sufficient. In addition, the required time from theheating start time to the Ba evaporation start time exceeds 11 seconds,so that it is again confirmed that the getter devices of ComparativeExamples are inferior in responsiveness.

EXAMPLES 10-11 AND COMPARATIVE EXAMPLES 5-6

These examples show results of operating the respective getter devicesin which the frequency at the time of the radio frequency inductionheating is changed from those of the respective getter devices ofExamples 7-10.

That is, 54 mass % of Ni material powder having an average grain size of4.5 μm in which a weight ratio of Ni powder having a grain size of 20 μmor more is less than 2 mass %; 35 mass % of BaAl₄ alloy material powderhaving an average grain size of 44 μm; and balance of BaAl₄ alloy powderhaving a grain size of 44-53 μm were blended thereby to prepare a powdermixture as a material for the getter material. The respective getterdevices were prepared by using 1.1 g of the material in accordance withthe following procedures.

Namely, 1.1 g of the material was filled into a metal container composedof a low-carbon steel plate having a thickness of 0.015 cm, and thefilled material was compacted at a compacting pressure of 800 MPathereby to prepare a getter device of Example 10.

While, 1.1 g of the material was filled into a metal container composedof a low-carbon steel plate having a thickness of 0.022 cm, and thefilled material was compacted at a compacting pressure of 800 MPathereby to prepare a getter device of Comparative Example 5.

The getter devices of Example 10 and Comparative Example 5 were heatedby radio frequency induction power having a frequency of 500 kHz. Whenthe radio frequency induction power for heating the getter device ofExample 10 was set to a level so that the time from the heating starttime to Ba evaporation start time was 9.5 seconds, a Ba evaporationamount of 228 mg was obtained after the heating operation for 30seconds.

On the other hand, when the getter device of Comparative Example 5 washeated by the same high frequency electric power as in Example 10, thetime from the heating start time to Ba evaporation start time was 11.6seconds, a Ba evaporation amount of 182 mg was obtained after theheating operation for 30 seconds. When the frequency (f) at this timewas applied to the relation formula: t≦12.7/(f)^(1/2), a thicknesslimitation of t≦0.018 (cm) was obtained.

Next, 1.1 g of the same material for the getter material as in Example10 was used for preparing the getter devices of Example 11 andComparative Example 6 in accordance with the following procedures.

Namely, 1.1 g of the material was filled into a metal container composedof SUS410 a ferrite type stainless steel plate having a thickness of0.02 cm, and the filled material was compacted at a compacting pressureof 1000 MPa thereby to prepare a getter device of Example 11.

While, 1.1 g of the material was filled into a metal container composedof a ferrite type stainless steel plate having a thickness of 0.03 cm,and the filled material was compacted at a compacting pressure of 1000MPa thereby to prepare a getter device of Comparative Example 6.

The getter devices of Example 11 and Comparative Example 6 were heatedby radio frequency induction power having a frequency of 250 kHz. Whenthe radio frequency induction power for heating the getter device ofExample 11 was set to a level so that the time from the heating starttime to Ba evaporation start time was 9.6 seconds, a Ba evaporationamount of 230 mg was obtained after the heating operation for 30seconds.

On the other hand, in case of Comparative Example 6, when the getterdevice was heated by the same high frequency heating electrical power asin Example, the time from heating start to Ba evaporation start was 11.7seconds, while the Ba evaporation amount after heating for 30 secondswas 177mg. In case of the frequency (f) of 250 kHz, when a platethickness (t) is calculated on the basis of the relation formula:t≦12.7/(f)^(1/2), the thickness relation: t≦0.0254 (cm) is obtained.

INDUSTRIAL APPLICABILITY

According to the present invention, since the temperature at which thepressed powder mixture starts the exothermic reaction is set within arange from 750° C. to 900° C., there can be provided a getter materialand an evaporation type getter device capable of suitably controlling anevaporation amount of getter components under a stable condition, and isexcellent in responsiveness because a time ranging from a starting timeof heating the getter material to a starting time of evaporation of thegetter components can be shortened. In addition, the metal container tobe filled with the getter material is free from deformation and melting,and a heat-evaporation process time of the getter material can beshortened, so that there can be provided the evaporation type getterdevice excellent in responsiveness because a time required for theelectron tube to attain to a predetermined vacuum degree can be alsoshortened.

1. A getter material configured by a pressed powder mixture comprisingBa—Al alloy powder and Ni powder, wherein when the pressed powdermixture is heated in a vacuum atmosphere or an inert gas atmosphere, atemperature at which an exothermic reaction starts is ranging from 750°C. to 900° C.
 2. The getter material according to claim 1, wherein theNi powder has an average grain size of 10 μm or less.
 3. The gettermaterial according to claim 1 or 2, wherein a ratio of Ni powder havingan average grain size of 20 μm or more with respect to an entire Nipowder is 10 mass % or less.
 4. The getter material according to any oneof claims 1 to 3, wherein the pressed powder mixture is apress-compacted body formed by press-compacting a power mixturecomprising the Ba—Al alloy powder and the Ni powder at a compactingpressure of 400 MPa or more.
 5. The getter material according to claim4, wherein the press-compacted body has an electrical resistivity of 20mΩ-cm or less.
 6. An evaporation type getter device comprising: a metalcontainer; and a getter material according to any one of claims 1 to 5,the getter material being filled in the metal container.
 7. Theevaporation type getter device according to claim 6, wherein the metalcontainer filled with a getter material is formed of at least onematerial selected from of Fe, Ni, Fe alloy and Ni alloy, and whenassuming that a plate thickness of the metal container is t cm while afrequency of alternate current magnetic field for heating andevaporating Ba component from the getter material is f Hz, the platethickness t of the metal container and the frequency f of alternatecurrent induction field satisfy a relation formula: t≦12.7/(f)^(1/2). 8.An evaporation type getter device comprising: a metal container formedof at least one material selected from of Fe, Ni, Fe alloy and Ni alloy;and a getter material configured by a pressed powder mixture comprisingBa—Al alloy powder and Ni powder that are filled in the metal container,wherein when assuming that a plate thickness of the metal container is tcm while a frequency of alternate current magnetic field for heating andevaporating Ba component from the getter material is f Hz, the platethickness t of the metal container and the frequency f of alternatecurrent induction field satisfy a relation formula: t≦12.7/(f)^(1/2). 9.An electron tube equipped with the evaporation type getter deviceaccording to any one of claims 6, 7 and 8.